A few minutes after noon on Dec. 14 last winter, as Snowbird skiers celebrated the opening of Mount Baldy for the first day of the season, the cry rang out: “Avalanche!” A slab of snow the width of a house had broken loose from a traverse atop the Utah resort and was charging downhill. Witnesses shouted warnings to a lone skier below on Fields of Glory, but there was no escape.

Heather Gross, a 27-year-old pass holder from Salt Lake City, was the first of four people killed by inbounds avalanches at U.S. ski resorts last winter—the deadliest inbounds avalanche season in more than two decades. “It was a tough year,” says Ethan Greene, director of the Colorado Avalanche Information Center.Experts blamed unseasonal weather that destabilized the early snowpack.

A series of warm, dry spells followed snowstorms in November, creating a weak base for the big December storms that followed. “It was the classic ‘bricks on potato chips’ scenario,” says Doug Abromeit, director of the U.S. Forest Service’s National Avalanche Center.

Last season, slopes were sliding from the Sierra to the Wasatch to the Rockies. Jackson Hole resort closed for two days during the busy holiday period due to dangerous conditions. “When the snow came, it was constant and unrelenting,” says resort spokeswoman Anna Olson. The Christmas storms seemed like a gift for skiers, but they were a headache for safety directors.

On Dec. 25, Randy Davis and a friend grabbed first chair on Squaw Valley’s Red Dog lift and dropped into Poulsen’s Gully. Visibility was low due to blizzard conditions, and the two skiers took separate lines, so nobody witnessed the avalanche that swept Davis, a 21-year-old competitor and coach, through a stand of old-growth trees, causing fatal head injuries.

One third of avalanche victims die of trauma. For Abromeit, that statistic settles the helmet debate: “It’s a good idea to protect your head if you’re going into steep terrain.” Avalanche experts recommend that resort skiers consider wearing avalanche safety gear if they plan to hit extreme or isolated terrain on powder days. However, these devices “are not a protective shield,” says Dale Atkins, director of training and education for Recco, a company that specializes in avalanche rescue systems.

Thirty-one-year-old David Nodine wore a beacon to Jackson Hole on Dec. 27. At 1:25, as he hiked up Toilet Bowl to retrieve his skis, which had released following a jump, the slope tore away from the mountain. Patrollers quickly pinpointed Nodine’s location with a beacon search and extricated him from beneath seven feet of hard debris, but the Jackson local never regained consciousness.